How to import AC3D files?
You can use majic79's Blender-AC3D addon. It is a port of the one that existed for Blender 2.49 and the author seems to update it every now and then.


  What is it?
  It's a few python scripts to import/export AC3D data into and out of Blender 2.63+. For earlier Blender 2.6x versions you need an older revision of the plugin (https://github.com/majic79/Blender-AC3D/tree/BL2.62)
  
  Known Issues:
  
  
  Exporter:
  
  
  Export packed .blend images is untested...
  It will either export everything, or everything that's selected. Default
  behaviour is to export everything, if you want to only export those items
  that you can see (ie, in the render scene), then select all those items and
  check the "Selection Only" option on the export dialog.
  There's an option "Export Render Layer" - ie, only export what's currently
  visible - this doesn't work, but is in the plan
  
  Importer:
  
  
  No ngons yet.